UNITED NATIONS, Aug 28 (Reuters) - A group of 43 U.N. peacekeepers in the Israeli-occupied Golan Heights have been detained by militants fighting the Syrian army, and the world body is working to secure their release, the United Nations said on Thursday.

The detained peacekeepers are from the Philippines and Fiji, a U.N. official told Reuters on condition of anonymity.

"During a period of increased fighting beginning yesterday between armed elements and Syrian Arab Armed Forces within the area of separation in the Golan Heights, 43 peacekeepers from the United Nations Disengagement Observer Force (UNDOF) were detained early this morning by an armed group in the vicinity of Al Qunaytirah," the U.N. press office said in a statement.

It added that another 81 UNDOF peacekeepers were being restricted to their positions in the vicinity of Ar Ruwayhinah and Burayqah.

"The United Nations is making every effort to secure the release of the detained peacekeepers, and to restore the full freedom of movement of the force throughout its area of operation," it said.

The U.N. Security Council, which was meeting to discuss the humanitarian situation in Syria, was also expected to raise the issue of the kidnapped peacekeepers, a council diplomat said.

The Quneitra crossing on the Golan is a strategic plateau captured by Israel in a 1967 Middle East war. Syria and Israel technically remain at war. Syrian troops are not allowed in an area of separation under a 1973 ceasefire formalized in 1974.

UNDOF monitors the area of separation, a narrow strip of land running about 45 miles (70 km) from Mount Hermon on the Lebanese border to the Yarmouk River frontier with Jordan. There are 1,223 UNDOF peacekeepers from six countries.

Before the Syrian civil war, now in its fourth year, the region was generally quiet and the peacekeepers had mostly found their biggest enemy to be boredom.

The force's personnel come from Fiji, India, Ireland, Nepal, Netherlands and the Philippines. The United Nations said this week that the Philippines has decided to pull out of UNDOF, and from a U.N. force in Liberia, which is struggling with an outbreak of the deadly Ebola virus.

Blue-helmeted U.N. troops were seized by militants in March and May 2013. In both of those cases they were released safely.

Austria pulled its troops out of UNDOF in 2013 due to the escalation of fighting. (Reporting by Louis Charbonneau; Editing by Chizu Nomiyama, Jonathan Oatis and Tom Brown)